Method of plasma etching

ABSTRACT

A plasma etching system using a ground electrode made of silicon carbide and a cover made of a dielectric material not containing aluminum, where the cover is laid over the substrate electrode, thereby preventing aluminum from being produced out of these parts and reducing device damage. Namely, a plasma etching system has a substrate electrode mounted in a vacuum process chamber, a ground electrode and a plasma generating source, and uses plasma to provide etching of substrates mounted on said substrate electrode. The plasma etching system is characterized in that the ground electrode is made of carbon or silicon carbide, and the dielectric material containing a Si compound covers the surface portion of the substrate electrode facing inside the substrate installation portion of the vacuum process chamber, except for the substrate installation portion.

[0001] This application is a Divisional application of Ser. No.09/866,702, filed May 30, 2001, which is a Continuation application ofSer. No. 09/487,303, filed Jan. 19, 2000.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a plasma etching system using aplasma for etching of substrates mounted on a substrate electrode. Morespecifically, this invention relates to a plasma etching system whichuses chlorine gas (Cl₂) alone or hydrogen bromide gas (HBr) alone, or amixture of chlorine gas (Cl₂) and oxygen gas (O₂) or of hydrogen bromidegas (HBr) and oxygen gas (O₂) as an etching gas to provide siliconetching.

[0003] A microwave plasma etching system, for example, is known whichuses chlorine gas (Cl₂) alone or hydrogen bromide gas (HBr) alone, or amixture of chlorine gas (Cl₂) and oxygen gas (O₂) or of hydrogen bromidegas (HBr) and oxygen gas (O₂) as an etching gas to provide siliconetching.

[0004] To prevent substrates from being contaminated by iron (Fe),chromium (Cr) and nickel (Ni), a microwave plasma etching system usesaluminum as the material of the electrode having a ground potential(ground electrode), in place of the material containing theseimpurities. To prevent the electrode from being damaged or worn by achlorine gas (Cl₂) plasma or hydrogen bromide gas (HBr) plasma, thesurface of the aluminum (Al) is further treated with anode oxidation(aluminized treatment). To prevent the substrate electrode from beingdamaged or worn, the substrate electrode, except for the substrateinstallation portion, is covered with aluminum oxide (alumina), whichacts as a dielectric material.

[0005] Prior plasma etching systems do not take into account themetallic contamination by aluminum (Al) generated out of the componentsof the etching process chamber. Metallic contamination of substrates byaluminum (Al) resulting from etching has occurred in recent highlyintegrated devices, especially the devices containing minute gates,thereby causing the interface state to be increased.

SUMMARY OF THE INVENTION

[0006] An object of the present invention is to provide a plasma etchingsystem in which it is possible to avoid metallic contamination byaluminum (Al) as well as metallic contamination by iron (Fe), chromium(Cr) and nickel (Ni), and to suppress device damage.

[0007] Aluminum (Al) contamination has been found to be caused by aground electrode made of aluminum (Al) and the cover (alumina) laid overthe substrate electrode, according to an analysis made by the presentinventors, namely, according to an evaluation of metallic contaminationusing total reflection X-ray fluorescence spectrometry.

[0008] This shows that the object of the present invention can beachieved by using a ground electrode made of silicon carbide and a covermade of a dielectric material that does not contain aluminum (Al) wherethe cover is laid over the substrate electrode. This prevents aluminum(Al) from being produced out of these parts.

[0009] The present invention is characterized by a plasma etching systemcomprising a substrate electrode mounted in a vacuum process chamber, aground electrode and a plasma generating source, wherein plasma is usedto provide etching of substrates mounted on the substrate electrode. Inaccordance with the invention, the ground electrode is made of carbon orsilicon carbide, and a dielectric material containing a Si compoundcovers the surface portion of the substrate electrode facing inside thesubstrate installation portion of the vacuum process chamber, except forthe substrate installation portion itself.

[0010] The present invention prevents metallic impurities (Fe, Cr. Niand Al) from being generated out of the components of the etchingprocess chamber, thereby reducing device damage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a vertical cross sectional view of a microwave plasmaetching system representing one embodiment of the present invention;

[0012]FIG. 2 is a transverse sectional view of the etching processchamber in FIG. 1;

[0013]FIG. 3 is a cross sectional view of a substrate immediately beforeetching by the system in FIG. 1;

[0014]FIG. 4 is a cross sectional view of a substrate immediately afteretching by the system in FIG. 1;

[0015]FIG. 5 is a vertical cross sectional view of a microwave plasmaetching system representing another embodiment of the present invention;

[0016]FIG. 6 is a transverse sectional view of the etching processchamber in FIG. 5; and

[0017]FIG. 7 is a diagram showing the relationship between the groundelectrode and substrate installation surface of the substrate electrodein accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0018] One embodiment of the present invention will be described withreference to FIGS. 1 and 2.

[0019]FIG. 1 is a cross sectional view of a microwave plasma etchingsystem, while FIG. 2 is a transverse sectional view of the etchingprocess chamber in FIG. 1.

[0020] Microwaves generated by magnetron 1 are transferred to waveguide2 and launched into etching process chamber 4 through bell jar 3. Theetching process chamber 4 comprises the quartz bell jar 3, a substrateelectrode 5, a quartz-made electrode cover 6 and silicon carbide-madeground electrode 7. The electrode portion of the substrate electrode 5is made of a material containing aluminum. The etching process chamber 4incorporates a magnetic field generating DC power supply 8, a solenoidcoil 9 and a gas supply unit 10.

[0021] Gas fed to the etching process chamber 4 from the gas supply unit10 is turned into a plasma by the electric field formed by the microwave(electric field) and the magnetic field formed by the direct currentsupplied to the solenoid coil 9 from the magnetic field generating DCpower supply 8. A substrate 11 is etched by the plasma. The etchingpressure is controlled by a vacuum exhaust unit 12. The energy of theions incident on the substrate 11 is controlled by the radio-frequencypower supplied to the substrate electrode 5 from a radio-frequency powersource 13.

[0022]FIG. 3 is a cross sectional view of a substrate immediately beforeetching by the system in FIG. 1. The substrate 11 has an oxide film 15and a polycrystalline silicon layer 16 formed on the silicon substrate14, and mask 17 is patterned on the polycrystalline silicon layer 16. Amixture of Cl₂ and O₂ is used as the etching gas. The etching gas isturned into a plasma by the magnetic field and microwave electric field,and the polycrystalline silicon layer 16 of the substrate 11 mounted onthe substrate electrode 5 is etched by ions and radicals in the plasma.In this case, the energy of the ions in the plasma incident on thesubstrate 11 is controlled by radio-frequency power having a frequencyof 800 Hz supplied from the radio-frequency power source 13.

[0023]FIG. 4 is a cross sectional view of a substrate immediately afteretching. When the oxide film 15 is etched upon completion of etching ofthe polycrystalline silicon layer 16, the incident energy of ions in theplasma is reduced by decreasing the radio-frequency power supplied fromthe radio-frequency power source 13 in order to control the yield of theetching of the oxide film 15.

[0024] The present invention uses the quartz-made electrode cover 6 andthe silicon carbide-made ground electrode 7 to ensure that iron (Fe),chromium (Cr), nickel (Ni) and aluminum (Al) as metallic impurities ofthe substrate are not generated from the electrode cover 6 and groundelectrode 7 at the time of etching.

[0025] As disclosed above, the present invention prevents metallicimpurities (Fe, Cr, Ni and Al) from being generated out of thecomponents of the etching process chamber.

[0026] Another embodiment of the present invention will be described.

[0027] Similarly to the previous embodiment, this embodiment uses themicrowave plasma etching system shown in FIGS. 1 and 2 to etch thepolycrystalline silicon gate structure. The substrate 11 before etchinghas an oxide film 15 and polycrystalline silicon layer 16 formed on thesilicon substrate 14, as shown in the cross sectional view of FIG. 3.The mask 17 is patterned on the polycrystalline silicon layer 16. Amixture of HBr and O₂ is used as the etching gas, and the etching gas isturned into a plasma by the magnetic field and microwave electric field.The polycrystalline silicon layer 16 of the substrate 11 is etched byions and radicals in the plasma. In this case, the energy of the ions inthe plasma incident on the substrate 11 is controlled by the 800 kHzradio-frequency power supplied from the radio-frequency power source 13.

[0028]FIG. 4 is a cross sectional view of the substrate 11 immediatelyafter etching. In order to control the yield of etching of the oxidefilm 15 upon completion of etching of the polycrystalline silicon layer16, the energy of incident ions in the plasma is reduced by decreasingthe radio-frequency power supplied from the radio-frequency power source13. The quartz-made electrode cover 6 and the silicon carbide-madeground electrode 7 are used to ensure that iron (Fe), chromium (Cr) ornickel (Ni) and aluminum (Al) as metallic impurities are not generatedfrom the electrode cover 6 and ground electrode 7 at the time ofetching.

[0029] As disclosed above, the present invention prevents metallicimpurities (Fe, Cr, Ni and Al) from being generated out of thecomponents of the etching process chamber.

[0030] Still another embodiment of the present invention will bedescribed with reference to FIG. 5 and FIG. 6.

[0031]FIG. 5 is a cross sectional view of a microwave plasma etchingsystem. FIG. 6 is a transverse sectional view of the etching processchamber in FIG. 5.

[0032] Microwaves generated by the magnetron 18 are transferred towaveguide 19 and launched into the etching process chamber 21 throughquartz-made window 20. The etching process chamber 21 is composed of aquartz-made inner cylinder 22, an aluminum-made vacuum vessel 23, asubstrate electrode 24, the quartz-made electrode cover 25 and thesilicon carbide-made ground electrode 26. Gas fed from the gas supplyunit 29 is turned into a plasma by a microwave electric field and amagnetic field formed by the direct current supplied to the solenoidcoil 28 from the DC power supply 27. Substrate 30 is etched by theplasma, and the pressure during etching is controlled by the vacuumexhaust unit 31. The energy of the ions incident on the substrate 30 iscontrolled by the radio-frequency power applied to the substrateelectrode 24 from the radio-frequency power source 32.

[0033] Etching of the substrate 30 is carried out using the same stepsas those for the above disclosed embodiment. The etching process chamberis composed of a quartz-made inner cylinder 25 and a siliconcarbide-made ground electrode 26 to ensure that iron (Fe), chromium (Cr)or nickel (Ni) and aluminum (Al) as metallic impurities are notgenerated from the electrode cover 25 and ground electrode 27 at thetime of etching.

[0034] These measures according to the present invention avoidcontamination by metals (Fe, Cr, Ni and Al) coming out of the componentsof the etching process chamber.

[0035] The above embodiment has been used to explain the effect of usinga quartz-made electrode cover. The same effect can be obtained when asilicon nitride cover is used.

[0036] To control the energy of ions incident on the substrate, it ispreferred that the ground electrode is clearly visible from thesubstrate electrode; in other words, the ground electrode preferablyshould have a sufficient area. As shown in FIG. 7, it is preferred tomeet the conditions of Es/Ws>2, where the substrate area is Ws, and theground electrode area is Es. If the substrate area Ws is increased, thepreferred ground electrode area must be increased accordingly. From theview point of the ground area, there is no upper limit to the ratioEs/Ws, but the ratio Es/Ws is limited by other structural restrictionsof the etching process chamber.

[0037] As shown in FIG. 7, the bottom end face of the ground electrodeis preferably almost as high as the substrate installation surface ofthe substrate electrode, or extended slightly below the installationsurface. By way of example, the height of the ground electrode h isabout 45 to 70 mm. The ground electrode as a whole preferablyconstitutes a part of the inner wall of the vacuum process chamber atthe inclined upward position on the outside in the radial direction ofthe substrate installation surface of the substrate electrode.

[0038] Radio-frequency power supplied to the substrate electrodedescribed with reference to this embodiment is preferably not to exceed2 MHz, or is more preferably within the range from 400 to 800 kHz. Thesame effect can be obtained even when time modulation bias is applied tothis radio-frequency (13, 32).

[0039] The effect of the microwave plasma etching system has beendescribed with reference to this embodiment. The same effect can also begained according to other discharging methods, for example, Helicon Typeand TCP (Transform Coupled Plasma) methods.

[0040] As disclosed above, the present invention prevents metallicimpurities (Fe, Cr, Ni and Al) from being generated out of thecomponents of the etching process chamber, thereby suppressing devicedamage.

What is claimed is:
 1. A method for plasma etching a substrate,comprising: placing the substrate, to be plasma etched, in a processingchamber having a ground electrode and a substrate electrode, thesubstrate being mounted on a portion of the substrate electrode; andgenerating a plasma in the processing chamber, in an etching gas, andetching the substrate by said plasma, wherein the ground electrode ismade of carbon or silicon carbide, and wherein a dielectric materialcontaining a silicon compound covers a portion of the surface of thesubstrate electrode, except for the portion of the substrate electrodeupon which the substrate is mounted.
 2. The method according to claim 1,wherein the etching gas includes at least one of chlorine and hydrogenbromide gas.
 3. The method according to claim 1, wherein said substrateincludes silicon to be etched.